How to Create Unique Column With Jpa

JPA - @Column (unique=true) - What is really point of having 'unique' attribute?

unique in @Column is used only if you let your JPA provider create the database for you - it will create the unique constraint on the specified column. But if you already have the database, or you alter it once created, then unique doesn't have any effect.

How to create a JPA entity for a table that doesn't have a Primary Key or Unique Key column

Let's assume you wanted to change those records with SQL. How would you know which row to update or delete if you don't have a unique column?

Unless you create a unique column, there's nothing you can do about it.

JPA How add unique contraint on column for @OneToMany relation like on username

Let the user have a Site reference:

@ManyToOne(optional=false)
private Site site;

Now add the constraint to user:

@Table(uniqueConstraints = {
    @UniqueConstraint(columnNames = { "username", "site" })})
@Entity
public class User{
// etc
}

You will also have to change the Site mapping:

@OneToMany(mappedBy="site")
private List<User> users;

Why can't i update an entity when it has a unique constraint on a column

Finally it's working! It fixed itself(still don't understand). Anyways , thanks for your suggestions.

How to Set Unique Column As forgeinKey In Jpa Mapping

A foreign key constraint can be created by referring to either primary key or unique key of the parent column.

The entities can be saved either using child object or a parent object since its a bidirectional relationship. However link both the objects before saving.

Please choose the approaches according to your use case.

Saving using Address entity

Customer customer = Customer.builder().email("abc").name("name")
                .build();
        Set<Address> addressSet=new HashSet<>();
        Address a1 = Address.builder().address("addressname").customer(customer).build();
        addressRepository.save(a1);

Saving using Customer Object

    Set<Address> addressSet = new HashSet<>();
        Customer customer = Customer.builder().email("abc").name("name")
                .build();
        Address a1 = Address.builder().address("addressname").customer(customer).build();
        addressSet.add(a1);
        customer.setAddresses(addressSet);
        entityRepository.save(customer);

To avoid the issue object references an unsaved transient instance - save the transient instance before flushing please add the cascadetype accordingly.

 @ManyToOne(fetch = FetchType.LAZY,cascade=CascadeType.ALL)
    @JoinColumn(name = "customer_email",referencedColumnName = "email")
    private Customer customer;